Arterial blood filters can be used in conjunction with a heart/lung machine during open heart surgery, along with a number of other devices. The purpose of this equipment is to take over the function of the heart and lungs during open heart surgery so that the heart can be repaired with very little interference by the peritoneal blood, thereby providing a clear field for the surgeon. The arterial filter is the last device through which the blood passes before being returned to the patient. The function of the arterial filter is to remove air emboli and other foreign matter that may be present in the blood, so that these foreign substances do not enter the patient's vascular system.
There have been a number of arterial blood filters on the market over the past years. These filters are generally similar in materials and construction, although the geometry of the designs vary considerably.n In general, these prior art devices utilize polycarbonate resin for the housing because of the need for high impact resistance to adequately resist the impacts and abuse which may be experienced during the elimination of trapped bubbles in the priming process by tapping on the devices to dislodge the bubbles. The filter media is generally monofilament polyester screen in the 20-43 micron pore size range and is sandwiched with an inner and outer layer of polypropylene netting before being pleated and formed into a cylindrical pack. The function of the netting is to lend mechanical stiffness to the pleated pack. The pleated filter media packs are set into the housing with a potting compound, which is generally an olefin hot melt or polyurethane. The housing parts are joined together by a variety of methods, including spin welding, ultrasonic welding, hot plate welding, electromagnetic fusion, and screw type assemblies.
The assemblies generally include a blood inlet and a blood outlet. The blood inlets are in various positions and attitudes. Some of the inlets take the form of a connector which is tangent to the outer cylindrical wall of the housing, thus causing a vortex type flow for the purpose of forcing bubbles to the center and top of the filter housing where they can exit the filter through a vent fitting. The U.S. Pat. No. 4,411,783 to Dickens et al, issued Oct. 25, 1983, is an example of such an assembly. Other designs of arterial blood filters make use of an axial inlet which is at the top of the filter, the blood entering and flowing in an end to end path to an outlet connector at the bottom. The U.S. Pat. No. 4,056,476 to Mouwen et al, issued Nov. 1, 1977 is an example of an arterial blood filter having axial inlets and outlets and a vent disposed at the inlet end of the assembly.
Several problems are encountered in prior art arterial blood filter assemblies which demand improvement. Of primary importance is the venting of air emboli from the filter housing. The air emboli must be efficiently removed from the housing, and foreign matter trapped by the media, while hemolysis must be avoided. Additionally, it is necessary that the external blood circuit outside of the patient's body must consume as little blood volume as possible in order to not deprive the patient of the patient's own blood volume and require additional blood, saline or other volume enhancers to be fed into the patient's cardiovascular system. Hence, it is critical that the arterial blood filter have the minimum possible blood volume.
The present invention provides a novel and efficient means for enhancing the removal of air emboli from the filter assembly. Additionally, the specific construction of the assembly results in a minimum internal volume of the blood filter assembly.